Jim Grant's Tech Tips
Toyota Celica 2.2l DOHC, Rough Idle Problem
Q: This ‘90 Toyota Celica 2.2 liter with
DOHC came to me with a very unstable idle. When I pull forward and hit
the brakes the idle will bounce from 300 to 1200RPM continuously. The
car has heavy exhaust fumes that will burn your nose and eyes! There are
also multiple skips at idle, but the car runs good on the highway. The
02 sensor shows a lean problem. There are no codes in the ECM, the fuel
pressure is good, vacuum is low (15hg.) no vacuum leak found. The car
runs better with the return fuel line pinched. If I pull the EGR full
open, the car will just idle higher but not change in running pattern.
I have tested all of the major sensors, checked for interference from
the alternator. Where should I go from here? I have been working on cars
for 15 years plus, but this one tells me everything I learned is wrong.
would suggest a close inspection of the valve timing/timing belt. It sounds
as if the timing belt may have jumped a tooth or 2 causing one or both
of the camshafts to lose timing. The low engine vacuum is also another
indicator of valve timing problems. The vehicle’s computer will do one
heck of a job at hiding that type of condition, sending a tech chasing
his/her tail. Been there, done that.